This application relates to a scroll compressor wherein there are three discharge valves arranged about distinct compression chambers, and wherein a back pressure chamber taps a refrigerant from a central full discharge compression chamber.
Scroll compressors are known, and typically include a pair of scroll members each having a base and a generally spiral wrap extending from the base. The two wraps interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and as the orbiting occurs, the compression chambers are reduced in volume, thereby compressing an entrapped refrigerant.
There are many challenges for scroll compressor designs. One challenge relates to a force tending to separate the wrap of each scroll compressor from the base of the other. The wraps must be maintained in sealing contact with the opposed base to maximize efficiency. However, the entrapped refrigerant does create a separating force.
To address the separating force, it is known to tap a partially compressed refrigerant to a back pressure chamber defined behind the base of one of the two scroll members. In practice, and for various reasons, it has typically been the case that the tap has been from an intermediate pressure chamber. There have been inefficiencies and concerns when a full discharge pressure refrigerant is tapped to the back pressure chamber.
Another feature which is known in scroll compressors is the use of a central discharge port associated with the discharge valve, but in addition, “over-pressure control valves.” These valves are positioned slightly radially outwardly of the central discharge port, and these valves can open and allow the refrigerant to enter a discharge plenum. Generally, when these over-pressure valves open, then the compressor could be said to be operating at a low pressure ratio. At other times, the compressor may be operating at a high pressure ratio, and only the central port will open.
A refrigerant system designer would understand that a scroll compressor will self-regulate in combination with an associated refrigerant system to operate either in a low pressure ratio or high pressure ratio conditions.
In scroll compressors, there are many design concerns. One design concern could be called “over-shoot.” Over-shoot occurs (see FIGS. 4A and B) when there is no provision of the over-pressure valves, and the refrigerant is compressed until it reaches the central compression chamber, at which time the discharge valve opens, and the refrigerant is now at a higher pressure than in the discharge pressure chamber. Thus, power is wasted to move the compressed refrigerant to that final compression chamber. The over-pressure valves as mentioned above, do address this concern.
However, another concern is backflow. When the refrigerant operates at the high pressure ratio, there is a concern that the compressed refrigerant, reaching a high pressure, can overcome the intermediate pressure refrigerant in the back pressure chamber, and cause the scroll members to separate. As shown in FIGS. 4B and 4C, one can understand the efficiency losses due to backflow and this concern.